Charles S. answered • 10/29/12

Algebra, Geometry, Statistics, AP Calc, GMAT, CFA, ACT, SAT, GRE Math

I think you have to remember what speed is. Speed is distance over time, which is why it is measured in miles per hour. And most students remember the formula rate = distance / time from middle school. The question gives you info about speeds and times, but not about distance, so once we figure that out, we can get everything else. So if r = d/t then distance = rate * time. We don't know either rate, but we do know they are 75 apart. And we know the distances are the same, so think something like:

distance = speed of commercial * 2.5

and

distance = speed of private * 6

and you know:

speed of commercial = 3*(speed of private) - 75

so you can do one equation that is:

2.5(3r - 75) = 6r (and here r represents the speed of private jet)

Solve for r (I'll leave this part up to you) and you should get something 300 mph for commercial jet and 125 mph for private jet. And, of course, because its almost as fun as six flags, you go back and check your work (125*6) = 750 = 2.5(300) and you go back and read the last sentence of the question to make sure you answer the question asked and don't let your teacher ding you for those 1 or 2 points b/c you didn't answer the question they asked. (Think speed of each jet -- yes I did!)